Gemini

Series of 12 two-person spacecraft launched into Earth orbit by the U.S. between 1964 and 1967, following the one-person Mercury program and before the three-person Apollo program. Designed to test astronauts' ability to maneuver spacecraft manually, the Gemini series helped develop techniques for orbital rendezvous and docking, procedures that were required later in the Apollo Moon-landing missions. It also gave NASA engineers a chance to improve spacecraft environmental control and electrical power systems.

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